Let a tumbler be half-filled with water, and fit upon its surface a
piece of white paper, upon which pour wine; then carefully draw out
the paper, say with a knitting-needle, so as to disturb the liquids as
little as possible, and the water, being the heavier, will continue at
the lower part of the glass; whilst the wine, being the lighter, will
keep above it. But, if a glass be first half-filled with wine, and
water be poured over it, it will at once sink through the wine, and
both liquids will be mixed.